1. Field of the Invention
The present invention relates to a method of manufacturing floating type composite magnetic heads used for hard disc type recording media, and particularly to a method of manufacturing floating type magnetic heads of so-called MIG (Metal-In-Gap) type in which ferromagnetic metal thin films are provided in the vicinity of a gap for high density recording.
2. Description of the Background Art
Recently, there exists a great demand for miniaturization in a hard disc drive device, so that high density recording in recording media is one of important problems to be studied. Accordingly, metal thin film type magnetic discs with high coercive force (Hc) have been developed as recording media in place of conventional oxide type magnetic discs in which oxide is provided. A magnetic head adapted to such a magnetic disc of metal thin film type is disclosed in Japanese Patent Laying Open No. 62-295207, for example. A floating type magnetic head of MIG type (Metal-In-Gap type) is proposed in the literature. In the MIG type floating type magnetic head, a film of high saturation magnetic flux density material such as Sendust, amorphous magnetic alloy or the like is formed by sputtering on a surface, on which a gap is formed, of a floating type magnetic head of conventional monolithic type or composite type.
FIG. 14 is a perspective view illustrating external appearance of a head core of a conventional floating type magnetic head of MIG type. As shown in FIG. 14, a head core 3 includes a pair of core halves 1a and 1b. The pair of core halves 1a and 1b are abut against each other with nonmagnetic material interposed therebetween. The pair of core halves 1a and 1b are formed of oxide magnetic material such as ferrite. A magnetic gap g is defined between the pair of magnetic core halves 1a and 1b. A ferromagnetic metal thin film 2 formed of Sendust or the like is formed by sputtering or the like on a gap forming surface of the I type core half 1a having no coil groove. Ferromagnetic metal thin film 2 is thus formed only on the gap forming surface of core half 1a.
With the coercive force (Hc) of recording media of about 1200 oersted (Oe), especially about 1500 oersted (Oe), the recording ability and overwrite performance of head core 3 having such a structure as shown in FIG. 14 for the recording media are insufficient. Accordingly, a head core as shown in FIG. 15 is proposed. The head core 4 includes an I type core half 1a and C type core half 1b. Ferromagnetic metal thin films 6a and 6b are formed on the gap forming surfaces of both of core halves 1a and 1b.
Next, a method of manufacturing a floating type magnetic head employing a head core having such structure as shown in FIG. 15 will be described. FIGS. 16-23 are perspective views and cross sectional views sequentially indicating structure in respective manufacturing steps of a conventional floating type magnetic head.
First, as shown in FIGS. 16(A)(B), specular polishing is applied to upper and lower surfaces of a first substrate 5a and a lower surface of a second substrate 5b formed of Mn-Zn ferrite. Subsequently, a first thin film 6a is formed by sputtering or the like on the upper surface as a gap forming surface of first substrate 5a to be an I type core half. The first thin film 6a is formed of a ferromagnetic metal thin film, a gap spacer such as a SiO.sub.2 film or the like and a glass film for bonding. A second thin film 6b is formed by sputtering or the like on the upper surface as a gap forming surface of second substrate 5b to be a C type core half. The second thin film 6b is formed of a ferromagnetic metal thin film and a gap spacer such as a SiO.sub.2 film.
Next, as shown in FIGS. 17(A)(B), the first thin film 6a and the second thin film 6b are patterned. The patterning is performed by removing the first and second thin films 6a and 6b by ionmilling or the like. Subsequently, coil grooves 7 are formed at portions indicated with broken lines in second substrate 5b. Glass rod receiving grooves are formed at portions indicated with broken lines 8 in the second substrate 5b. Extra processing grooves are formed at portions indicated with broken lines 9 in the second substrate 5b. FIG. 18(A) is a partial sectional view illustrating the second substrate 5b before grooves are formed. FIG. 18(B) is a partial sectional view showing the second substrate 5b in which coil groove 10 and glass rod receiving groove 11 are formed.
As shown in FIG. 19, the first and second substrates 5a and 5b are abutted against each other so that the first and second thin films 6a and 6b face each other. A glass rod is inserted into glass rod receiving groove 11, and a glass layer 12 is formed by melting, flowing and solidifying the glass. Bonding the first and second substrates 5a and 5b with glass in this way, a block 14 is formed.
The block 14 is cut along the broken lines A--A'. Thus, a core block 15 at the slicing stage is formed as shown in FIG. 20. Oblique line portions 16 are cut off in the core block 15. Both of the cut faces are polished to produce a plurality of head cores 4 as shown in FIG. 21. Next, as shown in FIG. 22, a groove 18 is formed on the upper portion of head core 4. The width of a convex portion facing a medium 17, that is a track width T.sub.w is defined. Subsequently, as shown in FIG. 23, head core 4 is attached in and fixed to a slit 20 of a slider 19 formed of nonmagnetic material with a glass layer 21. The outer form of slider 19 is worked to complete the floating type magnetic head.
However, according to the above described conventional manufacturing method, problems as will be described below occur. In the processing steps of coil grooves 10 shown in FIGS. 17 and 18, second thin film 6b is directly cut by a diamond grinding wheel rotating at a high speed. The adhesive strength of the second thin film 6b to the second substrate 5b is weak. Accordingly, the second thin film 6b may be completely separated or may be raised from the surface of the second substrate 5b as shown in FIG. 24. As a result, the manufacturing yield of magnetic heads decreases. Also, the rise of second thin film 6b may cause false (secondary) gaps.
Furthermore, according to the above described method of manufacturing magnetic heads, the glass bonding shown in FIG. 19 is made by completely melting a glass rod inserted between a pair of core halves and flowing the melted glass into extra-processing grooves 13 and so forth. Accordingly, glass bonding temperature is higher than a softening point of glass by 150.degree. C. or more. As a result, the reaction proceeds at interfaces between the first and second substrates 5a and 5b, and first and second thin films 6a and 6b at the glass bonding process. Accordingly, there exists a problem that the false gaps are large.